Thank you for waiting. From the symptoms you've described, your guinea pig needs to be seen by a vet as soon as possible. Loss of appetite in guinea pigs, for any reason, is extremely serious. It is called anorexia. If they go for 24 hours without eating, a condition called ketosis develops and the guinea pig cannot recover. When a guinea pig exhibits lethargy and appetite loss, something serious is wrong. You’ll need a vet to diagnose exactly what it is. Here is where you can find a guinea pig/rabbit vet:http://www.rabbit.org/vets/vets.html
Until you can get to a vet, try to hand feed a variety of foods - a sprig of parsley, carrot, apple, a little piece of romaine lettuce. Be sure to leave the timothy hay in the cage, too, in case she decides to try eating it. You can read more about anorexia at these two sites:http://www.guinealynx.com/anorexia.htmlhttp://www.oginet.com/Cavies/cvanorx.htm
If there is nothing that will entice your guinea pig to eat, you can feed her from a syringe. You must make sure that she is passing stools before doing this because if she has a blockage, it's dangerous to force food into her system. To be sure, you can place her in a box on paper towels and watch for droppings. If she's defecating normally, you can make a slurry of crushed pellets, water, and pureed vegetables. This can be more difficult than it sounds, so I'm giving you a link to a page that describes it in great detail, including variations on what to feed, and how often to feed:http://www.guinealynx.com/handfeeding.html
There is a product called Oxbow Critical Care, available in pet stores, that would be even better than the homemade slurry. However, your time would be better spent in finding a vet.
It would also be good to give your guinea pig some unflavored Pedialyte (made for human infants), which you can buy in drug stores, discount stores, and many supermarkets. Continue running the vaporizor, too.
These measures may save your guinea pig's life in the short run, but they are first aid only, intended to keep up your guinea pig’s strength until you can get to a vet. The breathing difficulties may be signs of pneumonia, which is life-threatening all by itself. If you have further questions about this, just let me know by clicking on REPLY. I hope you're able to entice your guinea pig to eat and get him some assistance from a vet this evening.
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Edited by Anna on 2/9/2011 at 11:47 PM EST